Six Sigma DMAIC Process - Control Phase - Risk Assessment and Mistake proofing - Poka Yoke

Risk needs to be assessed on the “should-be” process to make the implemented solution more robust. Risk assessment of the new improved process makes sure that any potential effects of the possible failure modes do not result in loss of “holding of gains” over a period of time. Two key techniques to assess risk and make sure that no possible failures occur post control phase are:
  • Failure Modes and Effects Analysis
  • Mistake Proofing (or Poke Yoke)
Mistake Proofing – Poke Yoke:
Mistake proofing or poke yoke (derived from two Japanese words poka – inadvertent errors and yokeru – to avoid) helps de-link the Y’s from the X’s. Mistake proofing eliminates the potential for a problem to happen.

The key mistake proofing techniques are:
  • Shutdown – Shutdown or stop a process immediately on occurrence of a failure
  • Control – Eliminate the occurrence of failure in a process
  • Warning – Proactively notify the occurrence of failure in a process before it occurs
The three methods for prediction and detection approach are:
  • Contact method – Contact with the part in the process highlights the errors
  • Fixed-value method – Errors are detected in the process through counting
  • Motion-step method – Errors are detected by a motion or lack of it in the process



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